safety for electronic systems ESD Simulator Verification Greg

safety for electronic systems ESD Simulator Verification Greg Senko Business Manager - EMC Test Equipment Schaffner EMC Ken Wyatt Hardware Test Center Manager Agilent Technologies, Colorado Springs Copyright 2003 Schaffner EMC - All rights reserved Van de Graaff generator, Boston Museum of Science (photo © 2003 by Kenneth Wyatt)

safety for electronic systems 1. Virtually 2. Almost 3. We every EMC laboratory has one or more ESD simulator. none are equipped to verify the ESD simulators’ performance. will cover: 1. Verification techniques, including ISO, SAE, ANSI and IEC standards 2. Proposed changes in the measurement setup 3. Practical aspects of measurement setup and performance 4. Live demonstration 5. Copyright 2003 Schaffner EMC - All rights reserved

3 safety for electronic systems What parameters must be measured? Tip voltage Current waveform • Peak • Rise • Current at 30 ns • Current at 60 ns • Time Constant (air discharge, auto manf) • Current derivative - ANSI Draft (gives indication of smoothness) § Positive peak § Negative peak

4 safety for electronic systems Measuring tip voltage Measured at standard test levels: ± 2 k. V, ± 4 k. V, ± 6 k. V, ± 8 k. V, ± 15 k. V and ± 25 k. V Measured using Electrometer or Giga-ohm meter Most standards don’t specify requirements ISO 10605 specifies 100 GOhm minimum input impedance The simulator’s tip voltage not affected by the measurement If a Giga-ohm meter is used, the simulator must continuously charge the high-voltage capacitor - Many older simulators provide an initial charge only, which can bleed off with time or with load

5 safety for electronic systems Tip voltage measurement using Giga-ohm meter (Brandenburg Model 139 D)

6 safety for electronic systems Idealized ESD simulator waveform

7 safety for electronic systems Actual waveform measurement (Tek 7104)

8 safety for electronic systems How do we measure the current waveform? A low impedance shunt (ESD target) is used to represent a discharge into a large metallic object The shunt impedance is < 2. 1 Ohms Block diagram: CABLE TARGET ATTENUATOR OSCILLOSCOPE GROUND PLANE Optional Attenuator for > 8 k. V (20 d. B)

9 safety for electronic systems Typical ESD current measurement system NOTE: The reason a Faraday cage was written into the original standard was that the analog phosphor storage oscilloscopes were generally susceptible to the high field energy produced by simulators. The digitizing oscilloscopes today are much more immune and the Faraday cage is no longer a must. You must confirm your measurement system is unaffected, however!

10 safety for electronic systems Typical ESD current measurement system ESD measurement system at Schaffner, Switzerland.

11 safety for electronic systems Typical ESD current measurement system (Agilent lab) 1. 2 m ground plane clamped to ESD table.

12 safety for electronic systems Typical ESD current measurement system

13 safety for electronic systems Performing a contact discharge into the older ESD target Keytek MZ-15 EC Mini. Zap Simulator.

14 safety for electronic systems Target design history IEC 801 -2: 1991 • No longer referenced by any current ESD standard • No performance specifications • Poor design - lots of ringing IEC 61000 -4 -2: 1995 • Referenced by virtually all current ESD standards • No performance specifications • Transfer function “zero” at 5 -6 GHz ANSI C 63. 16 Draft 9 • Proposed new design (uses sm resistors and tapered transitions) • Flat to 6 GHz • “Driving” adapter to evaluate high frequency performance

15 safety for electronic systems IEC 801 -2 target “ball tip” Old design is no longer specified

16 safety for electronic systems IEC 61000 -4 -2 target Presently specified in standards The large flat disk tends to build up a pre-corona discharge, which slows the risetime and leads to variable results for airdischarge measurements. Example: EMCO CTC-3, and others

17 safety for electronic systems ANSI C 63. 16 target Proposed design Example: Schaffner MD-102, Amplifier Research CTR-2, and others

18 safety for electronic systems Old versus new ESD targets EMCO CTC-3 (left) Schaffner MD-102 (right).

19 safety for electronic systems New target with “driving” adapter to measure transfer characteristics Schaffner MD-102

20 safety for electronic systems ANSI C 63. 16 target specifications Reflection coefficient of target and adapter < 0. 1 • Equivalent to VSWR < 1. 22 Insertion loss < 0. 3 d. B up to 4 GHz Variation of attenuation of the target -attenuator-cable chain < ± 0. 3 d. B from DC to 1 GHz (< ± 3. 51%) < ± 0. 8 d. B from 1 GHz to 4 GHz (< ± 9. 65%)

21 safety for electronic systems Waveforms of IEC 801 -2 target vs. ANSI target IEC 801 -2 Target ANSI Target less HF ringing and shows true peak shape

22 safety for electronic systems Actual waveform measurement (Agilent 54855 A, 1. 5 GHz BW) Old target New Target

23 safety for electronic systems Actual waveform measurement (Agilent 54855 A, 6 GHz BW) Old target New Target

24 safety for electronic systems Choosing attenuators • Target transfer function is ~1 V/A when loaded by 50 Ohms • Contact mode peak current at 8 k. V is ~30 A • Input range of most oscilloscopes is < 10 V in 50 Ohm mode • Therefore, an attenuator is needed to reduce the signal level • 20 d. B is typically chosen for 10: 1 ratio • Contact mode to 25 k. V may require additional attenuation

25 safety for electronic systems Choosing attenuators • Low power attenuators may damaged by the short term peak power • Attenuators are available with 1 k. W peak power ratings • Use an 18 GHz attenuator with low SWR, < 1. 25 to 8 GHz • The attenuator accuracy requires that the entire chain be calibrated Accuracy variation d. B 0. 1 0. 3 0. 5 0. 7 0. 9 Percentage 1. 16% 3. 51% 5. 93% 8. 39% 10. 92%

26 safety for electronic systems Choosing cables • A low loss cable is required • Cable length < 1 m is required by most standards • Double shielding is required by most standards • The ANSI standard recommends RG 400 • RG 214 is twice the dia, 1/2 the loss and is commonly available

27 safety for electronic systems Oscilloscopes - Bandwidth All standards require at least 1 GHz bandwidth The BW/risetime of the oscilloscope is the single most limiting factor to accurately measure the pulse risetime The true risetime is related to the observed risetime as follows: The above correction is proposed in the ANSI draft standard and assumes a Gaussian rolloff in frequency response. However most digitizers use a sharper cutoff filter, 20 d. B/decade or higher.

28 safety for electronic systems Oscilloscopes - Bandwidth How does bandwidth affect observed risetime? Let‘s assume a Gaussian rolloff

29 safety for electronic systems Oscilloscopes - Sampling rate Single-shot sampling rate is the key • A fast-edge triangular peak requires fast sample rate • Risetime of 800 ps from 10%-90% is 80% of waveform • 10 Gs/s = 100 ps/sample • 8 samples in 800 ps or 10%/sample! • Since peak is symmetrical and somewhat rounded actual error is < 5% (assumes a triangle shape) Effective sampling rate increased by capturing multiple shots • Must have stable waveform • Useful for contact mode only - never for air discharge • Shot to shot variation is low for most simulators • Should be used for verification - not for calibration

30 safety for electronic systems Shot-to-shot variation - 20 shots 33. 3 A peak Std dev. 425 ± 0. 64% of peak 898 ps Rise Std dev 11. 9 ± 0. 66% of risetime

31 safety for electronic systems Oscilloscopes - Sampling rate SAE and ISO recommend 4 Gs/s minimum 2 Gs/s - 27. 87 A -16. 0% 10 Gs/s - 32. 23 A -2. 9% 5 Gs/s - 31. 92 A -3. 8% 20 Gs/s - 33. 18 A

32 safety for electronic systems Oscilloscopes – Interpolation - sin(x)/x ON or OFF? Interpolation ON Interpolation OFF 2 Gs/s - 27. 87 A -16. 0% 2 Gs/s - 29. 98 A -9. 6% 5 Gs/s - 31. 92 A -3. 8% 5 Gs/s - 32. 32 A -2. 6%

33 safety for electronic systems Calibrating the target-attenuator-scope chain It is recommended that the DC transfer function of the entire chain be measured as follows: • Inject a known current • Measure the resulting voltage at the oscilloscope • The attenuation factor = Injected current / observed voltage • Attenuation factor is used to correct waveform amplitude CURRENT SOURCE TARGET ATTENUATOR CABLE ATTENUATOR OSCILLOSCOPE GROUND PLANE Optional Attenuator for > 8 k. V (20 d. B)

34 safety for electronic systems Other factors - Do’s and don’ts Shielding • Do we need it? Position of ground cable • Will it affect waveform? Orientation of simulator • Will it affect waveform? Automatic Measurements • Must use Min and Max values to calculate 10% and 90% points Other cables • Keep them well separated

35 safety for electronic systems Oscilloscope shielding - Do we need it? Standards say yes, but probably not necessary - use distance test Scope inside Faraday cage Scope at corner of plane Scope next to simulator

36 safety for electronic systems Ground cable position Does affect results - peak, rise and duration Natural loop Loop closer to plane 20 Gs/s - 33. 6 A, 891 ps 20 Gs/s - 36. 9 A, 926 ps

37 safety for electronic systems Simulator orientation to target Does affect results - peak, rise and duration 20 Gs/s - 33. 6 A, 891 ps Simulator on axis 20 Gs/s - 33. 6 A, 913 ps Simulator tip down 10º 20 Gs/s - 34. 5 A, 945 ps Tip down 30º

38 safety for electronic systems Air discharge - What risetime/peak do you want? Approach speed and environmental factors will greatly affect results - not Repeatable! Obtaining a passing waveform is a matter of patience!

39 safety for electronic systems Measurement uncertainty The estimated bounds of the deviation of a measured quantity from its true value • List all the possible error sources and compute the uncertainty • Uncertainty budget for each measured parameter • Statement of confidence that can be placed in the value of uncertainty • Does measured result truly fall within acceptable limits? National Association for Measurement and Sampling publication NIS 81, The Treatment of Uncertainty in EMC Measurements Link to CE-Mag site http: //www. ce-mag. com/ARG/Senko. html

40 safety for electronic systems Target plane size ANSI - 1. 2 m x 1. 2 m, IEC 1. 5 m x 1. 5 m, ISO - N/A, SAE - N/A 20 Gs/s - 31. 85 A Mini Target Plane 1. 2 m 2 Target Plane 20 Gs/s - 33. 18 A

41 safety for electronic systems Demonstration equipment Simulator: Schaffner NSG 435 / Keytek Minizap MZ-15 EC New Target: Schaffner MD 102 (designed to new ANSI stnd) Old Target: Emco CTC-3 (designed to meet IEC 61000 -4 -2 stnd) Target Plane: Small sized plane for demo purposes Attenuator: Weinschel Model 2 -20, 20 d. B, 5 W, 1000 W peak Cable: RG-214 1 m Oscilloscope: Agilent Infiniium 54855 A 6 GHz BW, 20 Gs/s scope ESD Monitor: Credence Technologies CTC 034 -3 (counts and beeps for each ESD event) www. credencetech. com

42 safety for electronic systems Thank you for your attention Your feedback is welcome Greg Senko Business Manager - EMC Test Equipment Schaffner EMC Ken Wyatt Sr. EMC Engr Hardware Test Mgr Agilent Technologies (603) 642 -4694 gsenko@schaffner. com (719) 590 -2852 ken_wyatt@agilent. com